1. Field of the Invention
This invention relates to shaft couplings and, in particular, to splined shaft couplings.
2. Description of Related Art
It is known to provide a splined coupling between a hub and a shaft, comprising axial splines having flanks which transmit torque between the hub and the shaft and, further comprising a shoulder on the shaft at one end of the hub and a nut on the shaft at the other end of the hub whereby to clamp the hub axially against the shoulder. In such a coupling, it is not always possible to establish firm contact between the torque-transmitting flanks of the splines. As the amount of torque transmitted through splines has increased over the years, it has become apparent that the twist caused by the torque causes the ends of the splines to come into contact first. This greatly increases the stress at the ends of the splines, reducing their useful life. Additionally, it reduces the usefulness of the center of the splines, limiting the amount of torque that can be carried by that spline.
One solution to this problem has been to machine away some of the material that is caused to interfere by shaft twist. A guide to how much material to remove may be found by subtracting the tangential displacements of the male spline, typically ridges, for even loading from those of the female spline, typically mating grooves for the ridges. One way to remove the material causing the interference due to shaft twist is to introduce helical correction by machining the splines at a very small angle from true axial. Therefore, a shaft coupling having helical splines have been developed, such as that disclosed in U.S. Pat. No. 4,292,001, wherein a shaft coupling provides two relatively inner and outer members having a common axis, a means defining first surfaces provided on the respective members in circumferentially confronting relationship, a means defining second surfaces provided on the respective members in circumferentially confronting relationship and, the first and second surfaces extending at different helix angles relative the axis. As used in aircraft engine shaft coupling, this patent also provides a well known and conventional urging means for urging the members relatively axially such that the first and second surfaces co-operating to lock the members against relative axial movement and to impart to the members opposing circumferential forces urging the members into engagement at the first and second surfaces, respectively.